[Haskell-cafe] Restricted type classes

[David Menendez]

On Mon, Sep 6, 2010 at 10:22 PM, wren ng thornton <wren at freegeek.org> wrote:
> On 9/6/10 1:33 PM, David Menendez wrote:
>>
>> For that matter, can you even describe what pure is intended to do
>> without reference to<*>  or join?
>
> As already stated: fmap f . pure = pure . f

That's pretty general. For lists, the functions having that property
include const [], \x -> [x,x], and repeat.

In fact, I think *every* appropriately-typed function satisfies that
law. Does anyone know of a counter-example?

-- 
Dave Menendez <dave at zednenem.com>
<http://www.eyrie.org/~zednenem/>